Rooting of Rhododendron `Anna Rose Whitney' Cuttings as Related to Stem Carbohydrate Concentration

Abstract

Rooting of Rhododendron `Anna Rose Whitney' (R. griersonianum × `Countess of Derby') was delayed in cuttings from stock plants grown in full sun, compared to cuttings from plants grown in 80% shade. In the outer stem (extracambium tissues), concentrations of glucose, sucrose, soluble carbohydrate, and total nonstructural carbohydrates were higher in cuttings from shaded stock plants. In the inner stem (intracambium tissues), where rooting originates, fructose, starch, and nonstructural carbohydrates were lower in cuttings from the shaded stock plants. Rooting percentage was reduced by CO2 mist during propagation. At 7 days, during rooting with a CO2 enrichment to 1100 μl·liter-1, fructose in the inner stem was 3-fold higher than in cuttings rooted under atmospheric CO2 (340 μ1·liter-1). Under CO2 mist, total nonstructural carbohydrate concentration was higher in the inner stem throughout the rooting period. For both high stock plant irradiance and CO2 enrichment during propagation, there was an inverse relationship between fructose concentration in the inner stem and rooting. A possible mechanism for inhibition by fructose is proposed.